Hard Water - contains salts (usually calcium or magnesium) that interfere with formation of a lather from soap. Hard water used for irrigation of plants may leave white marks on foliage and the salts accumulate in the soil.

Hardy - of a plant able to survive the extremes of climate, often taken to mean resistance to cold and frost.

Haulm - the collective stems or tops of crop plants (e.g. beans, peas, potatoes, grains, grasses) after the crop has been gathered, as used for bedding or thatching. Occasionally applied to a single stem.

Hedge -
Hedgerow - a border, fence or boundary formed by a row of closely planted shrubs or bushes often trimmed to a formal shape. The number of species forming a hedge tends to increase in proportion to its age.

Heel - a small portion of the previous year's growth at the base of a cutting.

Hemicellulose - heterogeneous mixture of polysaccharides resembling cellulose, but of lower molecular weight and less complex. Hemicellulose is insoluble in hot water or with chelating agents, but can be extracted with dilute aqueous alkali. Present in allmost all plantcellwalls where hemicellulose binds with pectin to cellulose to form a network of crosslinked fibres, but found especially in woody tisues. Includes xylan, glucuronoxylan, arabinoxylan, arabinogalactan II, glucomannan, xyloglucan and galactomannan.